In order to provide drive in such an environment, use may be made of a motor designed to operate in a vacuum. The motor drives the load directly and the torque is limited to the motor drive torque.
There also exist speed reduction systems using step-down gear trains. These systems have the advantage of increasing the drive torque relative to the motor torque. For applications in a vacuum, such as in space, the choice of materials often limits utilizations because of the environmental constraints. Such systems are bulky and of considerable mass.
For applications in the earth's atmosphere, mechanisms including "harmonic drive" gearing can be used. These gearing systems enable considerable speed reductions to be obtained using a single, compact gear train. As a general rule these systems using fluid lubrication, which technology is highly satisfactory in such an environment.
However, in space applications, this technology runs a severe risk of polluting the surrounding parts of the drive mechanism.
Preferred implementations of the invention mitigate this drawback.